This invention relates to expanded or foamed shaped products with good flexural and compressibilityproperties comprising a select combination of starch and a hydrophobically modified acid anhydride or its hydrolyzed acid counterpart and the method of preparation thereof.
The use of plastic and thermoplastic materials such as polystyrene, polyethylene and polyurethane have dominated the custom foam packaging market in recent years. However, because of its biodegradability as well as other favorable environmental characteristics and its ready availability, starch and starch based products have received increased attention in the foam product area.
U.S. Pat. No. 5,035,930 issued Jul. 30, 1991 and U.S. Pat. No. 5,043,196 issued Aug. 27, 1991 disclose the formation of expanded shaped starch products by the extrusion of high amylose starch and include the addition of synthetics, such as polyvinyl alcohol, polyvinyl acetate and polyurethane to improve product properties. U.S. Pat. No. 5,248,702 issued Sep. 28, 1993 discloses expanded starch based products useful as packaging fillers which are fabricated by extrusion of starch in the presence of a particulate bubble nucleating agent such as silicon dioxide and amorphous silica. U.S. Pat. No. 5,314,754 issued May 24, 1994 is directed to a method of producing starch derived shaped articles wherein high amylose starch is extruded under selected temperature and pressure conditions.
European Patent 0 712 883 published May 22, 1996 discloses biodegradable, structural shaped products having good flexibility or rigidity properties which are provided by extruding starch having a selected large particle size and preferably containing a nucleating agent.
U.S. Pat. No. 5,252,271 issued Oct. 12, 1993 discloses a biodegradable packaging foam which is provided by extruding a non-modified starch which is admixed with a selected mild acid, water and a carbonate composition.
The state of the art, as exemplified above, has shown many different approaches to forming starch based foam products. However, because of the nature and characteristics of starch it has been difficult to produce foamed starch products which have good flexural, compressibility and surface properties such as gloss, smoothness and uniformity. Additionally, because of the various products and the many different types of applications available, there is always the need for improved products and methods of preparation. This is particularly true in the preparation of starch foam used in the formation of sheets, shapes and planks for packaging applications which require increased flexibility.